Call-distributing telephone system



Oct. 21, 1958 CALL-DISTRIBUTING TELEPHNE sYs'ml Filed lay 14, 1954 w R. V. JUDY THS v4 Sheets-Shut 1 Hs c:

POS 2 POS 2l, 1958 y R. v. JUDY CALL-.n's'mlunns TELEPHONE sys'mu f Fund nay- 14. 1954 4 Sheets-Sheet 2 mno OF Nuo OP Euobwo mmm. E. Nwm O... m

momdm mozmh y R. v. JUDY cALuDrs'mxBU'rmc '1-E1 .1-:1=HoNEv SYSTEM Oct. 2l, 1958 Fim; my 14. 1954 wm um n mozuzwb R. v; JUDY' cALL-nrs'rarsu'rms TELEPHONE sYs'rEu Oet. 21,L 1958 4 Shel'etS-FSheet 4 Filed lay 14. 1954'- United States Patent M CALL-DISTRIBUTING TELEPHONE SYSTEM Robert V. Judy, Chicago, Ill., assignor to International Telephone and Telegraph Corporation, a corporation of Maryland Application May 14, 1954, Serial No. 429,861

' 10 claims. (c1. 179-27) This invention relates to a call-distributing telephone system. The general object is to provide a new and improved system for distributing to idle attended specialservice operator positions the calls received on a group of special-service trunks.

Important features are that calls waiting on the specialservice trunks are answered in the order of their arrival thereon, and that such waiting calls are distributed se- `quentially to such of the attended special-service positions ras are idle.

` GENERAL DESCRIPTION It has been chosen to illustrate the invention as embodied in an automatic telephone system wherein a group of special-service trunks are accessible upon the calling of a special-service number assigned thereto, and wherein a group of special-service operator positions are assigned to answering calls over the special-service trunks. It may be assumed that the special service given over the noted trunks and positions is information service, which is used by those desiring to learn the telephone numbers of persons not yet listed in the directory, or of persons not listed in the local directory.

According to one feature of the invention, preferenceallotting apparatus is provided which defines a series of preference positions according to which waiting calls are answered in sequence, and preference-selecting apparatus is provided which assigns the unoccupied preference positions to the trunks in succession as the calls arrive thereon, vany such trunk thereby having the lowest-numbered unoccupied preference positionassigned thereto.

VAccording to another feature, position-allotting apparatus is'provided which defines an endless-chain order of succession to the operator positions and tests the positions in that order to select an idle one when any waiting call is to be answered, and switching apparatus'is provided to connect any such selected position to the trunk yon which the oldest unanswered call is waiting, asdetermined by the next preference position in the series.

Another feature is that the foregoing allotting, selecting, and switching operations occur automatically, respon- `sive to seizure of the special-service trunks through the -automatic switches, whereby the connections are extended telephonically to the respective positions without requiring the operators to perform any special acts.

A further feature is that the operator who has answered a call and has completed the concerned transaction can cause the connection to the special-service trunkY and to her position to be released forthwith, by the operation of a release key, without Waiting for the calling person to clear out'the connection.

According to a still further feature, any operator may cause any call she is handling to be transferred, byV

l'2,857,472 ce Y, y Patented-oct. 21,4 195s 2 utility when information is requested in a languageV with which the answering operator is not familiar but which may be familiar to the supervisory operators.

Other objects and features will appear hereinafter.

Of` the accompanying drawings, comprising Figs. 1 to 4, Figs. 1 to 3 illustrate one embodiment, and Fig; 4 illustrates a desirable modification.

Fig. 1 is a schematic single-line switching diagram of an automatic telephone switching system embodying the invention.

Figs. 2 and 3 are circuit diagrams of portions of th apparatus of Fig. l.

Fig. 4 is a circuit diagram of a modificationY of Fig. 2.

Y tailed description will now be given.

F ig. I-trzmking diagram Referring now to Fig. 1 of the drawings, a simplified single-line switching diagram of an automatic telephone switching system is shown in Yorder to more clearly set forth the invention. p

The upper portion of Fig. 1 illustrates, schematically, a telephone switching system of the well-known step-bystep type.

If, for example, the subscriber at A desires to call the subscriber at B, he lifts his handset (not shown), listens for dial tone; and dials the number of station B. A connection from line L1 is thereby completed which may include finder F1, otlice selector OS, thousands selector THS, hundreds selector HS, connector C1, to lineV L2. Each of the items F1, OS, THS,` HS, and C1 constitutes but one of a group of equivalentitems, according to the usual telephone-system practice. Finder F1, being idle and allotted, finds the calling line L1 and connects it to OS, whereat dial tone Yis returned in the usual manner. When the oice digit (5 for example) assigned to the local oice is dialed, selector OS selects the correspending level and selects an idle trunk therein, such` as the trunk to selector THS. When the thousands digit,

is dialed, selector THS similarly selects Van idle hundreds selector, such as HS. When the hundreds digit is dialed, selector'HS selects the corresponding hundreds group and selects an idle connector therein, such as C1.y When the tens and units digits are dialed, connector C1 selects the corresponding tens group and selects the called line L2 therein, followed by the called line being rung until answering occurs. The connection clears out when the handsets are replaced.

In the systemof Fig. l, special services are handled through a group of special second selectors exemplified by second selector SS. These selectors are reached om the first level of the oliice selectors OS. One of the levels selecting positions, being thus a 25-point homing switch. The switches PS1 to P825 have common access to links LK1 to LKZS over which the information calls pass. Each switch PS1 to P525 normally stands in its home position H, from which position it is advanced when a call arrives on the associated trunk T1 to T25. Any such switch searches over the links LK1 to LKZS in Each is illustrated as having a home position and twenty-tivesequence to nd` the lowest-numbered idle one, whereby the position of preference of the corresponding call is established.

`Preference allotter PRA is a -pointl1oming switch having, access to links LKI to-LKZS. Itspurpose is to allot and mark these links in sequence so as tocause the call finders CF1 to CFS to connectV with the unanswered ones of the links in regular order- During non-waiting intervals, P-RA standsin its home position H, from which it is'advanced, by the arrival ofra call, to-search for the lowest-numbered link LKI to LK25,whereat PRA stops; marks that' link; and waitsthereon until the call on the marked link `is answered.

Five operator positions POSl to P085 are provided for answering the calls on LKl to LK25, being provided with call-iinder switches CF1 to CFS for this purpose. Switches CF1 to CF5V have common access to links LKll to LK25, and they may be similar to switches PS1 to PS25, but do not require a home position.

PositionY allotter PAI has yaccess to positions POSl to POSS in regular order, and is usedv to allot idle ones of them in regular sequence.4 The call-finder CF1 to CFS at the currently allotted position is thereby started tovnd any link LKI to LKZS which has been allotted by preference allotter PRA.

Lamp panel LP is provided with lamps L1 to L25 which show unanswered calls on trunks T1 to T25 respectively. These lamps enable a supervisory'operator to decide at any time whether an eicient number of the positions POSl to POSS are attended.

The apparatus at the lower portion of Fig'. l is supervisory apparatus enabling selected calls received at the rst ive positions to be transferred to and handled at three supervisory position POS6 to POSS. Position allotter PA2 may be similar to PAI, and switches CFG to CFS may be similar to CF1 to CFS.

General operation .ItY the subscriber at A, for example, desires information service, he dials the assigned information number, such as 14. If the finder and oiiice selector F1 and O81 are used, OSI responds to the digit l to select an idle selector SS, and selector SS responds to the digit 4 to select an idle information trunk in ygroup SST, such as T1.

Lamp L1 on the lamp panel LP is thereupon lighted. Preference-selector PS1 now advances from rits home position and stops on the first idle link, such as VLKl, 'and marks that link in the bank of preference allotter PRA.

VCurrent drawn by lamp panel LP causes start wire ST1 to become energized. Allotter PRA is thereby started from its home position `(or its action is thereby continued if it is in a non-home position) to advance over its sets of preference conductors PRI to PR25 in search of the first link LKl to LKZS having an unanswered call thereon. In the assumed example that link is LKl.` PRA stops thereon; marks LK1 busy to the other switches PS2 to PSZS, marks link LKI as waiting inthe bank of call-iindc'rs CF1 to CFS; energizes start wire ST2; and waits until the marked link LX1 is found (and the call thereon answered) by CF1 to CFS in response to the energization of ST2. When a waiting link is found by a iinder CF1 to CFS, its condition is changed from waiting to answered, wherefore the preference allotter PRA will not again allot it, but the answered link is held busy to switches PS1 to P825 until the connection thereover is released.

If the rst position P051 is currently allotted, by PA1 being in position l, the call on link LK1 is found yby CF1 extending the connection to POSI.

When the call on trunk T1 is thus answered, lamp L1, of lamp panel LP is extinquished, and the marking of link LK1 in the bank of PRA is canceled. If no other calls are waiting the preference allotter PRA is returned to home position. Otherwise, the energization of ST1 is continued to cause allotter PRA to find and allot the next waiting link LKZ to LK25.

If a number of calls arrive over the trunks T1 to T25` within a short interval, the concerned switches PS1 to P525 place them on idle ones of the links LK1 to LK25` in regular order.

Figs. 2 and S-circuit diagram Figs. 2 and 3 are illustrating circuit diagrams of apparatus of Fig. l, comprising lamp panel LP, preference` i aliotter PRA, position allotter PA1, trunk T1, preference selector PS1, link LKl, call nder CF1, and the appa-I` The other trunks, preference selectors, links, nders, and position equipi.

ratus at operators position POSI.

ments of Fig. l may be similar to the respective illus-` trated examples. in multiples 1MU, ZMU, and SMU of Fig. l: Conduc-` tors 1MU are the link-l multiple in the banks of selector PS1 to P825; conductors ZMU are the link-1 multiple, f

in the banks of finders CF1 to CFS, and conductors SMU are the link-l multiple in the Vbanks of finders CF6 l to CFS.

Referring to position POSI, with lthat position at#r tended, plugs 364 and 365 are in jacks TIl and RI,` rer,

spectively, to connect the operators transmitter lT and' i a receiver R in the circuit. Then the in-service relay 336 stands operated from ground at transmitter jack TI, through transmitter T, one winding of induction coil' IC, winding of relay 336, and through retard coil RT to battery. By-pass condenser 361' cooperates with RT and 336 for the usual filtering purpose.

At its contacts 2, relay 336 prepares an operate circuit for start relay 333; at its contacts 3, it normally places an idle marking ground on wire S in the bank of position allotter PAI; and at its contacts 1,jit grounds wire Idle. in group PAA through back contacts 1 of switching .re--l lay 332, thereby operating .idle relay 321 of PA1. Wire Idle is common to all call nders CF1 to CFS, as indivcated, wherefore it is grounded to hold'relay 321 operated` when any position P081 to POSS is attended andidle.. Chain relay 322 is restored at any time when any posi-` tion POSZ to POSS is attended, as its circuit is opened atV contacts 4 of the relay 336associatedA with that posi-` tion. Contacts 4 of the illustrated'relay 336 are strapped' to prevent that relay from restoring relay 322, wherefore relay 322 is operated except when one of the-succeeding positions is attended.`

` Detailed operation to the selectors SS of Fig. l.

When a call arrives on trunk T1,'by the seizurel of that trunk by a selector SS of Fig. l, line relay 201 operatesV over the calling loop and conductors T and R of T1. It operates start relay 202 through the back contact. of cut` oif relay 203. At its contacts 5, start relay 202 preparesVV to apply marking ground to brush 216; at'its contacts 4,

it substitutes a holding ground potential onwirev SV of T1 J for theV normal idle-indicating `battery potential;, atits v contacts 6, it applies trunk-ring-tone current to wire T jr of trunk T1, from source TRT, via Vwire'208 and con'- denser `207; at its back contacts 1', it V.disconnects groundl from contacts 1 to 25 in the bank ofwhoming brrush'211;

at its front contact 1, it lights lamp L1 of lamp panel LP in series with pilot relay 205.

upper winding terminal of switching relay205.,

Stepping magnet 210 now operates-in a buzzer-likeA manner to advance brushes 2111- to 216 from home p osi-i;

Fig. 2 also shows the respective wires Y At its contacts f3, relay f. 202 connects motor magnet `210 to test brush 212'via backk contact 2Vof 205, and at its contacts 2, it grounds the.,

tion and over links LKI to LKZS (Figs. 1 and 2) until an idle link is -found. The stepping circuit is from ground encountered by brush 212, through back contact 2 of relay 205, contacts 3 of relay 202 interrupter contacts of 210, and winding of 210, to battery. When an idlev link (such as LKI) is reached, test brush 212 iinds no guarding ground on conductor S thereof, whereupon magnet 210 ceases to operate. Switching relay 205, which is short-circuited as long as brush 212 encounters ground, now operates in series with magnet 210.

At its contacts I, switching relay 205 further opens the homing circuit for motor magnet 210; at its contacts 2, it applies ground through brush 212 to conductor S of multiple IMU to mark link LKI busy to the selectors PS2 to P525 of Fig. l; at its contacts 3 and 4, it extends talking conductors T and R of trunk TI to the corresponding conductors of link LKI through brushes 213 and 214; at its contacts 5, it prepares a circuit for answer relay 204; and at its contacts 6, itV applies ground through brush 216 to wire M of group IMU, which is joined to wire S of group PRI, to mark link LKI as waiting in the bank of preference allotter PRA.

Pilot relay 250, at LP, operates in series with lamp LI to ground start wire ST1.

With the preference allotter PRA in its illustrated'home position, ground on ST1 operates the self-interrupted motor magnet 301, via brush 306 and contacts 2 of relay 302. With all non-home contacts of brush 306, grounded, magnet 301 continues to advance brushes 3&6 to 308 until shunted by a marking ground encountered by test brush 307. Variable resistor 304 is connected between the battery lead and magnet 301 to enable the magnet to ductor S of PRI is encountered by brush 307 thereby, closing a circuit through contacts I of relay 302 and variable resistor 305 to the junction of 301 and 304, thereby effectively shunting magnet 301 to stop the allotter on link LKI. Relay 302 now operates through brush 307, being adjusted so as not to respond to such motor-magnet current as may reach it through 305.

At its contacts I and 2, relay 302 opens the motormagnet circuit; at its contacts 4, it grounds start wire ST2; and at its contacts 3, it grounds brush 308, thereby grounding conductor M in group PRI, which continues as wire S in multiple ZMU. Link LKI is thereby marked as allotted in the banks of the call finders CF1 to CFS.

The position allotter PAI, although shown in a home position merely for convenience, normally stands on anl idle call-nderCFI to CFS. If it should be in its illustrated home position at a time when idle relay 321 is operated, as from CFI as described, and if chain relay 322 is then restored by virtue of a position P082 to POSS being attended (in addition to POSI), then motor magnet 324 is operated through contacts I of relays 321 to 323, to battery through 325.

When idle switch CF1 is reached, brush 327 finds ground on conductor S of group PA1, thereby shunting magnet through resistor 326 to stop its operation, resistors 326 and 325 corresponding to 305 and 304 of PRA. Relay 323 now operates as described for relay 302. Its contacts 1 and 2 disconnects magnet 324, and its contacts 3 extends the start wire ST2 to brush 328 in readiness for the next allotted call waiting on a link LKI to LKZS.

With the rst position POSI thus idle and allotted, the noted grounding of start wire ST2 by relay 302 eX- tends start ground through contacts 2 of the operated idle `relay 321, back Contact 2 of the unoperated chain relay 322, contacts 3 of the operated relay 323, brush 328, wire M in group PA1, contacts 2 of in-service relay 336, and through contacts 2 of relay 332 to start relay 333. Start relay 333 thereupon operates.

Unless the brushes 340 to 346 are already standing on the Vcurrently markedlink, as may happen during light 6 trac conditions, motor magnet 33 1 advances its brushes 340 to 346 to nd the link (LK1) marked by PRA. When the marked link LKI is found test brush 340 iinds ground on conductor S of ZMU, thereby shunting magnet 331 through resistor 338 to stop its operation, resistors 33S and 337 corresponding to 305 and 304 of PRA.

Switching relay 332 now operates as described for relay 302, through contacts 2 of relay 333 andl locks itself operated to wire 347. Wire 347 is normally grounded from ground at closed contacts 1 of relay 336, release key through break contacts of unoperated cutolT relay 335.

At its contacts 2, switching relay 332 restores start relay 333 thereby disconnecting 331 at its contacts 1 and 2; at its back contact I, it removes idle indicating potential from Idle wire of group PAA, and at its front contact l, it lights call lamp CL of operators position POSI to indicate to the attendant a call is waiting; at its back contact 4, it removes idle indicating potential from Wire S of group PA1, thereby allowing relay 323 to restore to allow the position allotter PAI to hunt for an idle attended operators position, and at its front Vcontact 4 ground potential is applied to wire 348. At its contacts 5 and 6, relay 332 extends talking conductors T and R of link LKI through talking condensers 362 and 363 to the operators talking circuit; and at its contacts 7, it applies ground potential through brush 343 to answer wire A of link LKI to operate answer relay 204 of selector PS1. The result of the closure of contacts 8 and 9 of relay 332 will hereinafter be described in connection with the transfer feature.

At its contacts 2, answer relay 204 further holds relay At its back contacts, the cutoff relay 203 releases startv relay 202 and at its front contacts further locks itself operated.

At its contacts 4, start -relay 202 upon restoring prepares a circuit to apply idle indicating potential to lconductor S of TI; at its contacts 6, it removes trunk-ringtone from conductor T of TI; at its front contact 1, it extinguishes lamp L1 and restores relay 250 if no calls are waiting; and at its back contact 1, it prepares a homing circuit for 210; and its ycontacts 5, it removes marking ground from brush 216.

The removal of ground potential from brush 216 'removes marking ground from Wire M of group IMU, and wire S of group PRI thereby restoring relay 302 of PRA. At its contacts 3, relay 302 upon restoring removes marking ground from wire M of group PRI; at its contacts 4 it removes ground from start wire ST2; and at its contacts I and 2 completes an operate path for 301. i

Motor magnet 301 thereupon operates to advance its brushes in search for the next marked link. If no calls Y are waiting preference allotter PRA returns to its normal illustrated home position.

When the operator at position POSI and the subscriber, who requested special service, have completed their transaction, the normal procedure is for the subscriber to replace his handset thereby restoring line relay 201 which restores cuto `relay 203. The operator upon completing the transaction operates a release key RK to restore the special-service apparatus. The operation of RK removes ground from wire 347 thereby restoring relay 332.

At its front contact 1, switching relay 332 extinguishes call lamp CL and at its back contact 1 it reoperates idle relay 321; at its back contact 4, it extends idle indicating ground to the bank of the position allotter over wire S; at its contacts 5 and 6, it opens the talking path; and at its contact 7, it removes ground from wire A, of link LKI to restore answer relay 204, of preference selector PS1..

At its conta-cts 3, answer relay 204 removes holding ground from sleeve conductor S, of special service trunk T1 thereby clearing out SS, OS and F1 thereby restoring line relay 201l if the subscriber has not replaced his hand-y set; at its contacts 2, it restores switching relay 205; and at its contacts 1,` it removes operating ground from relay 203 but relay 203 remains operated through its front contact until line relay 201 restores. y

The cutoi relay 203 remainsoperated under control of relay 201 to prevent the reoperation of start relay 202 during4 thehoming of the preference-selector switch.

Upon restoring, switching relay 205 disconnects specialservice trunk T1 from link LK1, and at its contacts 2, removes busy'indicated ground from wire S, of multiple 1MU, and at its contacts 1 completes the homing circuit for motor magnet 210 from ground atback contact 1 of start relay 202, contact 1 of 205, multipled contacts 1 to of thecontact bank associtaed with homing brushl 211, brush 211winding of 210, to battery. Motor magnet 210 advances its brushes 211 to 216 to their illustrated home position H, where brush 211 again applies idleindicating battery to the sleeve wire S of special-service trunk T1, thereby indicating T1 as idle to the selector SS. 'Ihe apparatus is then ready to receive a further call.

If position POS1 is the only position attended chain relay 322 is normally operated as previously described. With 322 operated, the operated path for 324 is open and the start ground on wire ST2 is extended directly to wire M of group PA1 thereby CF1 searches and nds all calls waiting on links LKl to LK25.

Call-transfer If an operator at positions POS1 to POSS receives a call in a language with which the operator is not familiar she may transfer the call to an idle supervisory position by operating a transfer key which causes the concerned call to appear at idle positions POS6 to POSS. The call is then automatically cleared from the original answering position. Positions POS6 to POSS are similarly equipped as POS1 to POSS.

If a call being handled at operators position POS1 is to be transferred, the operator operates transfer key TK which operates transfer relay 334, from ground at front contact 4 of operated switching relay 332, wire 34S, transfer key TK, winding of 334, to battery.

At its contacts 1, relay 334 locks itself operated to ground on wire 348, under control of the switching relay 332; at its contact 2, it applied ground through brush 345, wire M, which is joined to wire S of multiple 3MU, to mark link LX1 in the bank of call iinders GF6 to CFS; at its contacts 3 ground is applied to start wire ST3, being a wire similar to start wire ST2.

Ground on start wire ST3 extended through position allotter PA2 (Fig. l) to an idle call finder GF6, for example, starts the nder GF6 hunting for the marked link LKl.

When nder GF6 finds the marked link LK1, in the manner as described for CF1, switching relay 332 and in-service relay 336 of CF1 are operated.

At its contacts 9, switching relay 332, associated with call finder GF6, operates cutoi relay 335 of finder CF1.

The operate circuit for relay 335 is from ground at contacts 9 of switching relay 332, of call finder GF6, brush 346 of GF6, wire CG of multiple 3MU, wire CR, brush 344, contacts 8 of relay 332 of CF1, winding of 335, to

battery.

At its contacts, cutot relay 335 removes ground from wire 347 to restore switching relay 332 thereby releasing call nder CF1.

At its contacts 1, switching relay 332 lupon restoring applies ground potential to wire Idle of position allotter PAl; at its contacts 4, it restores transfer relay 334; at its contacts 2, it prepares an operate circuit for relay 333; and at its contacts 5 and 6 it opens the talking path to POS1.

It has been -chosen to illustrate the call finders CF1 to GFS as being similar, and it will be readily understood 8 t that in call finders GF6 to CFStheir associated transfer relay 334, cutoff relay 335, and the transfer key TK serve no utility.

' Contacts 9, of switching relay 332, brush 346, and

wire GG of multiple ZMU of call nders CF1 to CFSV are shown, but serve no utility.

The` operator at P036 upon completing the transaction with the subscriber clears out the connection in the manner as described for POS1.

F 4-crcut diagram modification Preference selector PS1 of Fig. 4, is a modification of the preference selector PS1 of Fig. 2.

Wires T and R of special-serviceV trunk T1", instead of being extended by contacts of the switching relay,

the preference selector switch, and links LKl to LKZS,

are extended directly to the banks of the call nder switches CF1 to CF5 over trunk multiple TM1.

When preference selector PS1' is not in use and is in its illustrated normal (home) position an idle-indicating potential is applied to sleeve conductor S of trunk T1' in the manner as described for PS1 of Fig. 2.

When a call arrives on trunk T1', by seizure of the trunk by a selector SS of Fig. l, line relay 401 operates over the calling loop and conductors T and R of T1'. It operates start relay 402 through the iback contacts of cutoff relay 403. At its contacts 4, start relay 402 pre; t pares to apply marking ground to brush 416; at its con. tacts 5, it substitutes a holding ground potential on conductor S of T1 for the normal idle-indicating poten` i tial; at its contacts 6, it applies trunk-ring-tone current` to wire T of trunk T 1', from source TRT, via wire 2031 and condenser 207; at its contacts 1, it disconnects ground from contacts 1 to 25 in the bank of homing brush 411;

at its contacts 3, it connects'motor magnet 410 to test4 brush 412 via back contact 1 of 405;r and at its contacts; 2, it grounds the .upper winding terminal of switching" relay 405.

Stepping magnet 410 now operates in a manner as` described for magnet 210 (Fig. 2) until test brush 412 nds no guarding ground on conductor S thereof, wheret upon magnet 410 ceases to operate.V Switching relay 405, which is shortcircuited as long as brush 412 en` counters ground, now operates in series with magnet 410.

At its contacts 1, switching relay 405 applies ground Y allotter PRA; at its contacts 3 the marking ground ex.

tended from allotter PRA over wire M of PRI', which is joined to wire S1 of MU, brush 417, contacts 3 of relay 405, wireS of trunk multiple TM1 to the call nders CF1 to CFS of Fig. 3.-

An idle call nder, selected by the position allotter, in the manner as described forV Fig. 3, finds trunk TM1 and extends the connection to the operators position and extends ground back over answer wire A of the multiple Y TM1 to operate the answer relay 404.

At its contacts 1, answer relay 404 operates cutoff relay 403 and further opens the homing Vpath for the switch; and at its contacts 2, it further grounds sleeve wire S of trunk T1'.

At its contacts cutoff relay 403 further locks itself operated and restores start relay 402.

At its contacts 1, start relay 402 upon restoring prepares a homing circuit for a motor magnet 410; at its contacts 4, it removes marking ground from wire S of group PRIl; at its contacts 6, it removes trunk-ring-tone from conductor T of trunk T1; at its contacts 5, it prepares to apply idle indicating battery to the sleeve kconductor S of the Tl'; switching relay 405.

Switching relay 405 upon restoring opens the operate circuit for lamp L1' and pilot relay 450 and'removes marking ground from conductor S of TM1.

Upon completing the transaction the operator operates her release key in the manner as described (for Figs. 2 and 3) thereby removing ground from the answer wire A of trunk multiple TM1 to restore answer relay 404.

At its contacts 2, answer relay 404 removes ground from the sleeve conductor S of trunk Tl; and at its contacts 1, completes the homing path for motor magnet 410.

Motor magnet 410 advances its brush to its illustrated homing position to apply idle indicating battery to sleeve conductor S.

The cutoff relay 403 remains operated under control of line relay 401 to prevent the reoperation of start relay 402 during the homing of the switch if the subscriber does not replace his handset thereby holding relay 401 operated.

The restoration of line relay 401 restores cutoff relay 403 therebyreturning the preference selector PS1 to its normal illustrated position.

It is contemplated that, in the modication shown in Fig. 4, a twenty-point switch will suice, instead of a twenty-ve-point switch as shown for Fig. 2, to handle the same amount of tra'ic.

The multiples 1MU' to SMU are multiples similar to multiples 1MU to 3MU of Fig. 2.

I claim:

1. In a switching system, rst-group lines, separate means for each rst-group line for placing a calling condition thereon, second group lines, means including circuit means for establishing a series of successive waiting positions for calling first-group lines, preferenceselecting means responsive to a calling condition being placed on any first-group line for selecting the first idle waiting position'in the series and for assigning that position to the calling first-group line, whereby successive ones of the waiting positions are assigned respectively to calling iirst-group lines in the order in which such lines are placed in calling condition, a preferenceallotter and means for operating it into association with assigned waiting positions in succession in the order of their assignment to respective iirst-group lines, switching means, and means controlled by the preference allotter when in association with any assigned waiting position for operating a portion of the switching means to connect an idle second-group line to the waiting rst-group line which has been assigned to such waiting position, the preference-selecting means comprising a separate preference selector for each first-group line, each preference selector having positions corresponding respectively to the established waiting positions, each preference selector having means for operating it into its positions in succession responsive to a calling condition on its associated rst-group line and for seizing the rst idle position encountered, means responsive to the said seizure for marking busy the corresponding position of each other preference selector and for marking the corresponding waiting position as occupied by a first-group line in calling condition.

2. In. a switching system according to claim l, each preference selectoncomprising a multi-brush stepping switch having successive sets of bank contacts comprising and at4 its contacts 2, it restores its positions, with means foradvancing its brushes ontol the contact sets in succession during a selecting operation, and means for causing the brushes to stand normally in a home position in fixed reference to the first set of bank contacts.

3. In a lswitching system, rst-group lines, separate meanshfor' each first-group line -for placing a calling condition thereon, second-group lines, means including circuit means for establishing a series of successive waiting positions for calling first-group lines, preferenceselecting means responsive to a calling condition being placed onany Erst-group line lforselecting the rst idle waiting position in the series and for assigning that position to thecalling iirst-group line, whereby successive ones of the Vwaiting positions are assigned respectively to calling first-group lines in the order in which such lines are placed in calling condition, a preference allotter and means for operating it into association withV assigned waiting positions in succession in the order of their assignment to respective first-group lines, switching means, and means controlled by the preference allotter when in association with any assigned waiting position for operating a portion of the switching means to connect an idle second-group line to the waiting first-group line which has been assigned to such waiting position, a position allotter and means for advancing it over the second-group lines in succession cyclically,` means for causing the position allotter to stop at and allot any idle second-group line encountered, means for causing the switching means to connect to a waiting first-group line only an idle second-group line which is then allotted by the allotting means, and means responsive to an allotted second-group line becoming connected to a lirstgroup line for marking that second-group line busy to the position allotter.

4. In a switching system, first-group lines, separate means for each first-group line for placing a calling condition thereon, second-group lines, means including cir-` cuit means for establishing av series of successive waiting positions for calling first-group lines, preference-selecting means responsive to a calling condition being placed on any iirst-group line for selecting the first idle waiting position in the series and for assigning that position to the calling rst-group line, -Whereby successive ones of the waiting positions are assigned respectively to calling Erst-group lines in the order in which such lines are placed in calling condition, a preference allotter and means for operating it into association with assigned waiting positions in succession in the order of their assignment to respective first-group lines, switching means, and means controlled by the preference allotter when in association with any assigned waiting position for operating a portion of the switching means to connect an idle second-group-line to the waiting rst-group line which has been assigned to such waiting position, wherein the said Ist-group lines comprise a group of special-service trunks to which respective connections are made through an automatic telephone switchboard, the said calling condition on any iirst-group line being dependent on the existence of said switchboard connection thereto, each rst-group line including relay means responsive to its calling condition to control the preference selecting means and to place a holding condition on the line to hold the associated switchboard connection, means at each rst-group line controlled from any second-group line with which it becomes connected for establishing and for subsequently terminating an answered condition at the rst-group line, and means including locking means responsive to the said termination of the answered condition at any first-group line for terminating the said holding condition thereon to permit-the switchboard connection to clear out and thereby free the trung comprising the last said first-group line.

5. In a switching system, first-group lines, separate means for each first-group line for placing a calling condition thereon, second-group lines, means including circuit means for establishing a series of successive waiting positions for calling rst-group lines, preference-selecting means responsive to a calling condition being placed on anyv rst-group line for selecting the rst idle waiting position in the series and for assigning that position to the calling rst-group line, whereby successive ones of the waiting positions are assigned respectively to calling rst-group lines in the order in which such lines are 11 placed in calling condition, a preference allotter and means'for operating it into association-with assigned waiting positions in succession in the order' of their assignment to respective first-group lines, switching means, and means controlled by the preference allotter when in association with any assigned waiting position for operating a portion of the switching means to connect an idle second-group line to the waiting rst-group line which has been assigned to such waiting position, thirdgroup lines, each second-group line including transfer means, means responsive to an operation of the transfer means of a second-group line in connection with a calling first-group line for applying a marking condition in reference to the connected tirst-group line, second switching means, means controlled by the said marking condition for operating a portion of the second switching means to connect an idle third-group line to the last said rst-group line, and means responsive thereto for freeing the last said second-group line while leaving the last said first-group and third-group lines connected together.

6. In a switching system, first-group lines, separate means for each Erst-group line for placing a calling condition thereon, second-group lines, means including circuit means for establishing a series of successive waiting positions for calling first-group lines, preference-selecting means responsive to a calling condition being placed on any first-group line for selecting the rst idle waiting position inthe series and for assigning that position to the calling rst-group line, whereby successive ones of the waiting positions are assigned respectively to calling first-group lines in the order in which such lines are placed in calling condition, a preference allotter and means for operating it into association with assigned waiting positions in succession in the order of their assignment to respective first-group lines, switching means, and means controlled by the preference allotter when in association with any assigned waiting position for operating a portion of the switching means to connect an idle second-group line to the waiting iirst-group line which has been assigned to such waiting position, links corresponding respectively to the established waiting positions, the means for selecting an idle waiting position comprising means for seizing the corresponding link and for connecting the concerned calling rst-group line thereto, and the switching means comprising means for connecting an idle second-group line to the link associated with, any waiting position with which the preference-allotting means is currently associated, whereby the second-group line is connected to the concerned rstgroup line through the last said link.

7. In a switching system according to claim 6, wherein the means for assigning a selected idle waiting position to a calling first-group line includes means for marking the assigned waiting position lbusy to the preference-selecting means and includes means for marking the assigned waiting position as assigned to the preference allotter, means responsive to the switching means connecting an idle second-group line to a link to which a waiting rst-group line is connected for marking the corresponding waiting position as unassigned to the preference allotter while maintaining it marked busy to the preference selecting means, means for subsequently disconnecting any connected link from the connected iirst-group and secondgroup lines, and means responsive to the disconnection of the link from the connected rst-group line for marking the corresponding waiting position idle to the preferenceselecting means.

8. In a switching system, iirst-group lines, separate means for each first-group line for placing a calling condition thereon, second-group lines, means including circuit means for establishing a series of successive waiting positions for calling rst-group lines, preference-selecting means responsive to a calling condition being placed on l2 Y anyiirst-group line for selecting the rst idle waiting position in the series and for assigning that positionjto ing positions in succession in the order of their assign ment to respective rst-group lines, switching means, and means controlled by the preference allotter when in association with any assigned waiting position for operating a portion of the switching means to connect an idle second-group line to the waiting first-group line whichghasf been assigned to such waiting position, the preference selecting means comprising stepping switches individual respectively to the first-group lines, the preference allotter comprising a stepping switch, and the said switching means comprising stepping switches individual respectively tothe second-group lines, each of said stepping switches having bank-contact positions corresponding rei spectively to the waiting positions.

9. In a switching system, rst-group lines, separatemeans for each first-group line for placing a calling condition thereon, second-group lines, means including circuit means for establishing a series of successive waiting posi- Y tions for calling first-group lines, preference-selecting means responsive to a calling condition being placed on any first-group line forselecting the tirst idle waiting position in the series and for assigning that position to the calling first-group line, whereby successive ones of the waiting positions are assigned respectively to calling first-group lines in the order in which such lines are placed in calling condition, a preference allotter and means for operating it into association with assigned wait-l ing positions in succession in the order of their assignment to respective first-group lines, switching means, and meansl controlled by the preference allotter when in `associationr with any assigned waiting position for operating `a portion of the switching means to connect an idle second-group line to the waiting first-group Vline which hask been assigned to such waiting position, the preference selecting` means comprising rst stepping switches individual re-` Y spectively to the first-group lines, the preference allotter. comprising a second stepping switch, and the said switching means comprising third stepping switches individual respectively to the second-group lines, each of the said iirst and second stepping switches having bank-contact positions corresponding respectively to the waiting posi-A tions, and each of the said third stepping switches having bank-contact positions corresponding respectively to thev first-group lines.

l0. In a switching system according to claim 1,'each first-group line and each waiting position including a separate marking conductor, the` preference selecting means including means for connecting the marking conductor ofv any assigned rst-group line to the marking conductor of thel waiting position assigned thereto, the preference allotter including means for energizing the marking conductor of any assigned waiting position with which it is associated, thereby energizing the marking l conductor of the first-group line to which the waiting posiv tion is assigned to mark such line as allotted, the said means controlled by the preference allotter comprising means responsive to the said energization of the marking i conductor of the allotted first-group line for operating a portion of the switching means to connect an idle secondgroup line to the allotted irst-group line.

i References Cited in the le of this patent f UNrTED STATES PATENTSV 1,816,634 calpenter et a1 July 2s, 1931 2,155,933

De Vriendt et al.` Apr. l5, `1,939 c 

